Field of the Invention
The present invention relates to a colored resin particle dispersion and an inkjet ink.
Description of the Related Art
The colorants for printing inks can be broadly classified into dyes and pigments. Using a dye offers the advantage of particularly favorable color development. Further, compared with pigments, dyes offer the advantage of superior abrasion resistance, and particularly superior rub fastness. However, dyes themselves exhibit inferior water resistance and marker resistance. On the other hand, pigments offer the advantages of high image density and excellent weather resistance, but exhibit inferior abrasion resistance, and particularly rub fastness, compared with dyes.
In light of these properties, a method has been proposed in which by encapsulating the colorant within a resin to form colored resin particles, an ink can be provided which exhibits excellent abrasion resistance, water resistance and marker resistance, while retaining the image-forming properties of the colorant. It is desirable that the resin has properties which impart the ink with abrasion resistance, water resistance and marker resistance.
Patent Document 1, Patent Document 2 and Non-Patent Document 1 each proposes the production of a polymer particle dispersion in which by using an organic solvent A and an organic solvent B having almost no compatibility with the organic solvent A, forming a dispersion composed of a dispersed phase containing the organic solvent B and a resin and a continuous phase containing the organic solvent A, and then removing the organic solvent B from the dispersion under reduced pressure or heating, a polymer particle dispersion is produced containing polymer particles dispersed in the organic solvent A.
In other words, a method is proposed in which a liquid, prepared by dissolving and incorporating within the organic solvent B a resin that does not dissolve in the organic solvent A, is dispersed within a continuous phase of the organic solvent A, and the organic solvent B is then removed under reduced pressure or heating, thus obtaining a polymer particle dispersion in which polymer particles are dispersed stably within the organic solvent A.
In terms of the resin for the dispersed phase, styrene-maleic acid copolymer resins are used in the examples of Patent Document 1, styrene-maleic acid copolymer resins and polyvinylpyrrolidone are used in the examples of Patent Document 2, and polyvinylpyrrolidone is used in Non-Patent Document 1. These resins include resins having polar groups that undergo negative dissociation and resins having polar groups that undergo positive dissociation, thus forming polymer particles having negative and positive charges, and providing stable dispersions.
Patent Document 3 proposes the production of a polymer particle dispersion in which by using an organic solvent A and an organic solvent B having almost no compatibility with the organic solvent A, forming a dispersion composed of a dispersed phase containing the organic solvent B, a polyfunctional monomer or resin and a polymerization initiator, and a continuous phase containing the organic solvent A, subsequently initiating a crosslinking reaction by light or heat, and then removing the organic solvent B from the dispersion under reduced pressure or heating, a polymer particle dispersion is produced containing polymer particles dispersed in the organic solvent A.
Based on the above documents, it is hoped that polymer particle dispersions will enable the stable dispersion of polymer particles from the nano level to the micro level, for use as coloring materials not only in inks and copy toners, but also within all manner of coating materials, colored liquid crystals, color filters for portable terminals, electronic books and electronic papers.
[Patent Document 1] JP 2007-197632 A
[Patent Document 2] JP 2005-255911 A
[Patent Document 3] JP 2007-197633 A
[Non-Patent Document 1] Japanese Journal of Polymer Science and Technology, Vol. 62, No. 7, pp. 310 to 315 (July, 2005)
However, no investigations were conducted in the above documents regarding the abrasion resistance, the water resistance and the marker resistance of images printed on paper or the like when a printing ink was prepared using the above types of polymer particle dispersions. Obtaining satisfactory abrasion resistance for the image simply by adding a resin is difficult. Further, a problem arises in that when a resin is used which provides improved abrasion resistance, water resistance and marker resistance for the ink, maintaining the stability of the dispersion is problematic. Moreover, when the colorant is added in an amount sufficient to obtain satisfactory color development in the printed image, a problem arises in that the viscosity of the polymer particle dispersion increases, making preparation of the dispersion difficult.
Further, the method of Patent Document 3 requires a polymerization reaction of the polyfunctional monomer or resin within the dispersed phase, meaning more production steps are required in producing the polymer particle dispersion.
On the other hand, when producing printed items using an ink containing colored resin particles, it is desirable that the color tone of the printed items does not change depending on the storage time or storage state of the ink. This type of change in the color tone of the printed items is particularly problematic when the ink is stored in a high-temperature environment in the period from ink production through until actual use.
An object of the present invention is to provide a colored resin particle dispersion and an ink which provide excellent abrasion resistance and prevent change in the color tone. Moreover, another object of the present invention is to provide a colored resin particle dispersion and an inkjet ink which exhibit excellent abrasion resistance, together with excellent water resistance and marker resistance.